Recently, to satisfy requirements for high speed straight running performance, high speed cornering performance, steering stability, rolling resistance and the like, belted radial tires having a low aspect ratio have been widely used for their high lateral stiffness, high cornering power and wide ground contacting width.
In such a low aspect ratio radial tire, however as the tire section height is relatively low, the radial distance of the inner face of the tread portion from the rim is short. Therefore, as shown in FIG. 10, when a large force F is applied to the tread, for example during running across a protrusion, the tire (t) is greatly deflected, and so called rim touch--an indirect contact of the inner face of the tread portion (a) with a flange of the rim (r) or a direct contact of the tread portion (a) with the bead portion (b)--is liable to occur. If rim touch occurs, the shock is directly applied to the car through the rim (r), and as a result, durability of the car, e.g. the suspension mechanism and the like is reduced.
To avoid this, the rigidity of the tire sidewall portion has been increased by increasing the rigidity of the carcass, providing a reinforcing layer, and/or increasing the rubber thickness of the sidewall portion especially on the axially inside of the carcass.
However, when the sidewall rigidity is increased in such a way, ride comfort is deteriorated. Further, once a tire whose rubber thickness is increased is deflected, the distance between the tread portion and bead portion becomes smaller than that being not increased, and rim touch occurs rather easily. Furthermore, the tire weight is increased to deteriorate the steering performance and running performance.